The present invention relates to a method of managing defects in a disk recording medium, an optical disk device recording data on the optical disk using such a defect management method, and an optical disk capable of storing information concerning a defect criteria used for replacing a defective area of disk with a non-defective area.
A very high degree of reliability less than 10xe2x88x9212 at worst is required of a disk used for recording computer data. Defect-managing systems have been used hitherto to accommodate the reality that defects in recording sectors which lead to an error are unavoidable, even very rare, in the current disk-manufacturing technique.
Disk mediums are subjected to the defect management for assuring data reliability even when dirt, scratches or degradation due to repetition of rewriting operation is caused. Primary defects occurring at the time of manufacture of the disks are found through a certifying process carried out at the time of initializing disks, and secondary defects occurring after being put to use are found through verification carried out at the time of writing, or the like. Sectors found to have a defect are replaced, using sectors located in a spare area formed on part of a disk other than a user area. In the defect management, a pair of a user area and a spare area is called a group.
In an example of arrangement of user areas and spare areas on a disk, the data area consists of a single group. However, there are many optical disks in which a data area is divided into a plurality of groups. When a defective group is found in a group, it is first attempted to replace the defective sectors using sectors in a spare area of the same group. In many cases, an optical disk is configured such that a recording capacity of a spare area is several % of that of a user area. The 90 mm magneto-optic disk standard defined by ECMA-154 or ECMA-201, and the DVD-RAM standard defined by ECMA-272 are examples of such configuration.
Incidentally ECMA is an abbreviation of European Computer Manufacturers Association, DVD is an abbreviation of digital video disk, and RAM is an abbreviation of random-access memory.
The presence or absence of a defect in a sector can be determined by an error in an ID signal representing a physical address of the sector, an error in a recorded data signal, or a servo error signal.
When a plurality of ID""s are recorded in the header area for each sector, if not less than a predetermined number of ID""s for each sector contain an error, the sector in question is found to have a header defect. In the DVD-RAM standard for example, each sector is provided with four ID""s, and an error can be detected for each ID. Each sector is found not to have a header defect if it has not more than two ID errors: a sector having three or more ID errors is found to have a header defect, since its reliability is low.
Further, the presence or absence of an error in a recorded data signal is detected by the use of an error correcting code added thereto. When more than a predetermined number of errors are included per unit of recording, the data signal is found to have a data defect. The xe2x80x9cunit of recordingxe2x80x9d may be a sector or a block constituted of a plurality of sectors depending on the span of an error correcting code (ECC).
In the DVD-RAM standard, data is recorded in sectors on a disk, and is subjected to error-correcting coding in units of 16 sectors, called an ECC block. Data of 32 KB constituting one ECC block is arranged in the form of matrix of 172xc3x97192 bytes (or 172 columnsxc3x97192 rows), and Reed-Solomon codes (inner code PI, outer code PO) of 10 bytes and 16 bytes are added in column direction and row direction, respectively, to constitute a product code.
The inner code PI is disposed so as to be completely within a sector. By means of the inner code PI, the number of error bytes in each row of the reproduced data can be determined. In accordance with the detected number of errors, reliability of each row is evaluated, and whether each sector or each block has a data defect can be determined based on the number. For instance, a sector including four or more rows having four or more error bytes is found to have a data defect, or a block including six or more such rows are found to have a data defect.
With regard to detection of defects based on a servo error signal, when the magnitude of the servo error signal such as a tracking error signal exceeds a predetermined value that makes it difficult to ensure the servo control stability required of data recording, a sector in question is found to have a servo defect.
When a sector is found to have a header defect, a data defect or a servo defect, it is found to be defective.
Generally, in the defect management, two different methods are used for performing replacement of a sector. One is a slip replacement, and the other is a linear replacement.
The slip replacement is applied to primary defects. If a defective sector is found at the time of certifying a disk, the next sector is used in place of the defective sector. In a disk drive device, for accessing a sector containing data, a logical address is converted into a physical address representing the position of the sector, and a sector having ID""s representing the physical address is accessed. When the slip replacement has been performed, the physical address numbers corresponding to the logical addresses are shifted, or xe2x80x9cslipxe2x80x9d by one.
The slip replacement is carried out within each group. For instance, if there occur two slip replacements of m sectors and n sectors in a user area, the end of the user area of the group is shifted into the head of the spare area by (m+n) sectors. If such slip replacements are made, the linking relation between the physical addresses and logical addresses is shifted by the number of replaced sectors for all the sectors succeeding the replaced sectors. Primary defects subjected to the slip replacement are registered in a PDL (Primary Defect List). The list contains the physical addresses of defective sectors in each entry.
Linking the physical addresses with the logical addresses can be made only when a disk is initialized, and therefore, the slip replacement is applied to primary defects only.
The linear replacement is applied to secondary defects. When a defective sector is found, replacement is effected using spare sectors in a spare area. When an ECC block (formed of 16 sectors) is found to contain a defective sector, the entire ECC block is replaced with 16 sectors in a spare area. There may be a case where a block in a spare area having replaced another block is subsequently replaced with another block. A substitutive sectors are given the same logical addresses as the original sectors.
The linear replacement is effected within the same group first. For instance, when two linear replacements of m blocks and n blocks respectively occur in a user area, m blocks and n blocks at the beginning of the unused part of the spare area are used. It may be so designed that when the spare area of the same group has been used up the spare area in another group is used. Secondary defects subjected to linear replacement are registered in an SDL (Secondary Defect List). The list contains physical addresses of defective sectors and substitutive sectors in each entry.
When such a linear replacement has been made, every time an access is made using a logical address which designated a substitutive sector, an access to the substitutive sector and subsequent return have to be made. Therefore, the average data transfer rate is substantially lowered when the secondary defects exist.
A set of the defect lists PDL and SDL is stored in a defect management area within a control information area in each of outer and inner periphery parts. They are disposed at a plurality of locations, and they are recorded together with information on the structure of a disk.
Generally, in recording devices, criteria for detecting primary and secondary defects are set in the following way.
A disk is at its best condition when primary defects are detected and registered. The number of defects on the disk increases with time or usage due to scratches and dirt, and resultant degradation. Therefore, the primary defects are detected and replacement is effected by using a criteria which is more strict than that for detecting the secondary defects, so that some additional scratches or dirt will not results in the finding of a defect according to the criteria for detecting the secondary defects.
Although the secondary defects are detected with a criteria which is less strict than that for the primary defects, a margin of safety is left between the criteria for detecting the secondary defects and the error-correcting capability, so as to ensure error correction during reproduction. In this way, different criteria are used for the primary defect detection and the secondary defect detection.
Conventionally, optical disks are used mainly for computer date recording, and therefore, the primary concern was to improve the data reliability, and defect management mainly consisting of replacement using spare sectors has been developed to deal with the defects in the recording sectors causing the errors.
In recent years, with increasing capacity of optical disks, their uses are expanding to the video recording field, such as in DVD.
Data files for recording computer data (PC files) are expected to be completely error-free, and high reliability is required of recording. In contrast, data files for recording audio or vide data (AV files) require recording data inputted continuously in real time. In some cases, errors are permissible as long as the disturbance of reproduced images or sounds is not noticed, so that data reliability is not required to be as high as in computer data recording. Instead, non-interruption of recording is important.
That is to say, with regard to storage devices for computer data recording, primary importance is the reliability rather than recording time, while, for storage devices for video recording, primary importance is continuous recording performance. Consequently, in case of using the same type of disk for recording both audio or video data and computer data, it is required to ensure reliability and recording speed which meet the requirements of the respective recordings. Likewise, defect management must be adaptable to both types of recording.
For carrying out replacement to deal with secondary defects of a disk at the time of recording, data is reproduced from the recorded part for verification, and if errors of more than a prescribed criteria, or a defective part from which reproduction is impossible is found, the data recorded in that part is re-recorded in substitutive sectors in a spare area, and data is again reproduced from the substitutive sectors for verification. Thus, when a secondary defect is detected, and replacement is effected, the time needed is four times more than the time needed for recording data once. In case of recording audio or video data in real time, it is likely that recording is interrupted if a defect is detected.
One solution to this problem is not to detect secondary defects during the recording of audio or video data. In this case, the reproduced image or the like may have disturbances at parts having the secondary defects, but such disturbances are considered less objectionable than interruption of recording. The underlying assumption is that once primary defects have been removed at the time of initialization of the disk, any secondary defects that might occur will be minor. If the scale of the secondary defects is greater than predicted, the disturbance of the reproduced picture may be intolerable, and thus this solution fails.
Where the optical disks are used for recording audio or video data, it is considered unnecessary to detect defects with criteria which is as strict as that used in recording computer data. This is because, if the excessively strict criteria is used, sectors which are permissible for audio or video data are also found defective, and video recording is interrupted when the time-consuming replacement is effected. Because the conventional defect management method does not take into consideration the intended use of the optical disk, and the criteria used is of the same level regardless of the intended use of the optical disk, there was no conception of using the optimum defect detecting method.
The present invention has been made overcome the above-outlined problem, and its object is to adapt defect management to the type of data recorded on an optical disk, or the intended use of the disk.
Another object is to improve the interchangeability of the optical disk.
A further object is to improve the utility of optical disks for recording audio or video data.
According to a first aspect of the invention, there is provided a method of managing defects on an optical disk used for recording data, including
determining a criteria for detecting defects according to the type of data for which defects are to be detected; and
detecting defects using said criteria when data is recorded on or reproduced from the disk.
With the above arrangement, it is possible to use the criteria suitable for the particular type of data for which defects are to be detected.
The step of detecting defects may be performed with regard to data recorded on the disk.
In this case the defects may be detected when the data is recorded on the disk, or when the data is reproduced for verification of the data having been recorded. When the defects are detected when the data is recorded, determination of presence or absence of servo defects and header defects can be made, but determination of presence or absence of data defects cannot be made. When the defects are detected during reproduction for verification, presence of absence of data defects as well as servo defects and header defects can be determined.
The step of detecting defects may alternatively be performed when the data is reproduced. In such a case, if defects are detected, the reproduction of the data is re-tried. Decision on whether the reproduction is to be re-tried is made using different criteria depending on the type of data being reproduced.
The method may further comprise the step of using non-defective areas of the optical disk in place of defective areas of the optical disk.
With the above arrangement, the result of the defect detection can be used in making a decision as to whether the areas found to be defective should be replaced with non-defective areas.
The step of determining a criteria may include:
selecting one of the plurality of criteria according to the type of data for which defects are to be detected.
With the above arrangement, the defect criteria can be determined simply by providing a signal which selects one of the plurality of criteria provided in advance, rather than specifying the values forming the criteria.
The plurality of criteria may include at least a first criteria, and a second criteria, the second criteria being less strict than said first criteria, and said step of selecting may include selecting the first criteria when the data for which defects are to be detected is one for which time restriction with regard to data recording or reproduction is less strict, and selecting the second criteria when the data for which defects are to be detected is one for which time restrictions with regard to data recording or reproduction is more strict.
An example of the data for which time restriction with regard to data recording or reproduction is less strict is computer data. An example of the data for which time restriction with regard to data recording or reproduction is more strict is audio or video data.
By using a less strict criteria for the audio or video data, interruption of the audio or video data recording is avoided unless the defect is of such a degree that the resultant disturbance in the sound or picture is intorerable.
The method may further include sending control information for specifying the criteria, from means for processing data to be recorded, to means for recording said data.
The above-mentioned means for processing data to be recorded is for example a host device. The above mentioned means for recording the data is for example a disk device.
With the above configuration, the host device can set criteria which is finely optimized for the type of the data to be recorded on the disk.
The data may be recorded in units of recording, and the step of sending control information may send the control information for each unit of recording.
With the above configuration, it is possible to dynamically set criteria which is finely optimized for each unit of recording (e.g., sector or ECC block), depending on the type of the data to be recorded in each unit of recording. That is, even when different types of data, e.g., audio or video data, and computer data, are both recorded on the same disk, since the host device sends the criteria control information in association with the data to be recorded, and the defect management can be effected using the optimum criteria for the respective data.
The control information specifying the criteria may select one of a plurality of criteria.
With the above configuration, the amount of control information is small, since it only needs to specify one of the plurality of predetermined criteria, rather than specifying values forming the criteria itself.
Data may be recorded in units of recording, and said method may further include recording control information representing the criteria for each unit of recording, on the optical disk, in association with each unit of recording.
With the above configuration, the criteria to be used for defect detection for each unit of recording (sector or ECC block) is known by reading the control information, and can be used for performing maintenance of the data recorded on the disk.
According to a second aspect of the invention, there is provided a disk device for accessing data on an optical disk, including:
means for determining a criteria for detecting defects according to the type of data for which defects are to be recorded; and
means for detecting defects using the criteria when data is recorded on or reproduced from the disk.
With the above arrangement, it is possible to use the criteria suitable for the particular type of data for which defects are to be recorded.
The detecting means may detect said defects with regard to data recorded on the disk.
In this case the defects may be detected when the data is recorded on the disk, or when the data is reproduced for verification of the data having been recorded. When the defects are detected as the data is recorded, servo defects and header defects can be detected, but data defects cannot be detected. When the defects are detected during reproduction for verification, data defects as well as servo defects and header defects can be detected.
The detecting means may alternatively detect defects when the data is reproduced. In such a case, if defects are detected, the reproduction of the data is re-tried. Decision on whether the reproduction is to be re-tried is made using different criteria depending on the type of data being reproduced.
The device may comprise means for managing defects on the optical disk by using non-defective areas of the optical disk in place of defective areas.
With the above arrangement, the result of the defect detection can be used in making a decision as to whether the areas found to be defective should be replaced with non-defective areas.
The determining means may include:
means for storing a plurality of criteria; and
means for selecting one of said plurality of criteria according to the type of data for which defects are to be detected.
With the above arrangement, the defect criteria can be determined simply by applying a signal for selecting one of the plurality of criteria provided in advance, rather than specifying the values forming the criteria.
The plurality of criteria may include at least a first criteria, and a second criteria, the second criteria being less strict than the first criteria, and the selecting means may select the first criteria when the data for which defects are to be detected is one for which time restriction with regard to data recording or reproduction is less strict, and selects the second criteria when the data for which defects are to be recorded is one for which time restriction with regard to data recording or reproduction is more strict.
An example of the data for which time restriction with regard to data recording or reproduction is less strict is computer data. An example of the data for which time restriction with regard to data recording or reproduction is more strict is audio or video data.
By using a less strict criteria for the audio or video data, interruption of the audio or video data recording is avoided unless the defect is of such a degree that the resultant sound or picture is intolerable.
The determining means may determine the criteria according to a control signal supplied from outside of the device.
The control signal may be supplied from a host device connected to the disk device.
With the above configuration, the host device can set criteria which is finely optimized for the type or contents of the data for which defects are to be detected.
The device may further comprise means for recording data, in units of recording, on the disk,
wherein
said determining means may determine the criteria for each of the units of recording, and
the recording means may also record criteria control information controlling the criteria for each unit of recording, in association with the each unit of recording.
With the above configuration, the criteria to be used for defect detection for the data of each unit of recording (e.g., sector or ECC block) is known by reading the control information, and can be used for performing maintenance of the data recorded on the disk.
According to a third aspect of the invention, there is provided an optical disk for recording data, including an area storing criteria control information specifying criteria to be used for detecting defects for data recorded on or reproduced from the disk.
With the above configuration, the criteria to be used for detecting defects when the disk is accessed is known by reading the criteria control information recorded on the disk. Accordingly, the maintenance of the data on the disk is facilitated, and the interchangeability of the disk is improved since the criteria control information can be read by any disk device.
The data may be recorded in units of recording, and the criteria control information indicating the criteria to be used for detecting detect with regard to the each unit of recording may be recorded in association with the each unit of recording.
With the above configuration, the criteria to be used for each unit of recording, e.g., sector or ECC block, is known by reading the criteria control information, and can be used for performing maintenance of the data recorded on the disk.
The information may select said criteria from a plurality of predetermined criteria.
With this configuration, the amount of control information is small, since it only needs to specify one of the plurality of predetermined criteria, rather than specifying values forming the criteria itself.